As circuit geometries become smaller and more complex, signal speeds become faster, and modular substitution of IC components become common, diagnostic and safety testing becomes more challenging. Automatic Test Equipment (ATE), for example, including integrated ATE systems, are used to generate signals to exercise and test a circuit or system. The resulting generated signals may be analyzed by the ATE and/or external test equipment. ATEs often require adaptation to a particular Device Under Test (DUT) within a particular integrated circuit (IC). The ATE-generated test signals may include a plurality of fixed reference sources for each of, for example, fixed thresholds (e.g., minimum or maximum thresholds) for a plurality of signal tests.
FIG. 1 shows a prior art system for testing a single diagnostic analog signal 12′ in which nodes 5a′ and 5b′ along a resistor string 10′ of resistors 10a′-10c′ deliver fixed reference/threshold output voltages 14a′ and 14b′ that are compared to diagnostic signal 12′. The diagnostic signal 12′ is compared to reference signals 14a′ and 16b′ at comparators 20 and 22 respectively. A diagnostic signal that falls outside either of the reference signals 14a′ or 14b′ will result in positive fault signals 20a′ or 22a′, and a subsequent positive fault signal 24′ from OR gate 24.
If the components of FIG. 1 were to be replicated for each diagnostic test, manufacture of such a system can become unwieldly if a DUT requires many tests or the tests need to be modified to adapt to changing or substituted circuitry.